Detented optical encoder

ABSTRACT

A detented encoder, employed for sensing a rotation of a wheel by a user between detent position, and suited for use in a pointing device or other user input device. The detented encoder includes a light emitter, a pair of photodetectors, and a codewheel. Interruption of light emitted by the light emitter and received by the photodetectors is processed by a logic circuit to produce a quadrature signal indicative of the detent position of the wheel. The codewheel is integral to a shaft that is supported at one end by a support bracket connected to the lower case of the device. The wheel rotates the shaft when turned by a user. The shaft includes a plurality of evenly-spaced, longitudinally extending spline teeth. A biasing member or opto spacer is operatively coupled to the lower case and includes a base portion on which the light emitter and photodetector are mounted. The biasing member includes a cantilever portion. A U-shaped slot in the cantilever portion includes a protrusion that engages the spline teeth on the shaft. The protrusion is biased against the splined portion of the shaft, so that as the shaft is rotated, the protrusion moves in and out of spline wells defined between adjacent spline teeth, thereby creating a detent action. The detented encoder also includes a microswitch that is activated by the shaft when a user depresses the wheel. A logic device processes the signal produced by the photodetector to determine the transitions between the detent positions as the wheel is turned.

FIELD OF THE INVENTION

The present invention generally concerns an input device, and inparticular, an input device that enables a user to manipulate a cursoror other graphic object, make selections, and control a computer.

BACKGROUND OF THE INVENTION

Pointing devices, such as computer mice and trackballs, are used toprovide user input to a computer program and are well known in the art.Such pointing devices enable a user to easily move a cursor on a displayscreen, and are fundamental to programs and operating systems thatemploy a graphical user interface, such as the Microsoft Corporation'sWINDOWS™ and Apple Corporation's MACINTOSH™ operating systems. In atypical pointing device, a ball is rotated in the housing of the device,either directly by the user's fingers, or by movement of the device overa surface. Depending upon its direction of rotation, the rotating ballin turn causes one or both of a pair of encoder shafts in the housing torotate. The encoder shafts rotate about a pair of orthogonal axes, i.e.,the “X” and “Y” axes in response to the components of the ball'srotation along those axes. As the encoders are rotated, they producesignals that indicate the device's incremental motion along theseorthogonal axes; these signals are processed by a driver programexecuting on a computer, which produces a corresponding stream ofdigital values indicative of a position of the device relative to the Xand Y axes. The driver program also receives other input signals fromthe pointing device, including a signal indicative of the state ofcontrol buttons on the device. The relative position data and the stateof the buttons are input to a computer program (or the operatingsystem), which processes the information, causing a predefined action tooccur. For example, many operating systems move a cursor displayed on amonitor or other display screen in response to a user's movement of apointing device. The X and/or Y movement of the cursor on the displayscreen is proportional to the motion of the ball (or device) along therespective X and/or Y axes.

In recent years, mouse manufacturers have added a third input axis totheir products, commonly known as the “Z” axis. Originally developed bythe Microsoft Corporation for use with its WINDOWS™ operating system,this axis on a mouse is primarily used for scrolling within a documentor displayed data. The Z-axis control on a mouse is typicallyimplemented as a detented wheel (the Z-wheel), which is coupled to anencoder that monitors rotation of the Z-wheel by a user. Detents on therotational motion of the wheel enable a user to scroll a document ordata display in consistent increments specified by the user, such as apredetermined number of lines/detent, or a screen/detent. The Z-wheel istypically mounted vertically and disposed toward the front of a mouse sothat it can be readily turned with a user's finger. The detent positionsare typically spaced at increments of about 20 degrees.

In order to obtain a desired level of performance, the output signalproduced by the Z-axis encoder should accurately correspond to thenumber and direction of detent positions that the user rotates theZ-wheel. For example, if a user rotates the Z-wheel through five detentpositions in a forward direction (rotating the top of the Z-wheel towardthe front of the mouse), this movement should be reflected by thecomputer program, e.g., by the program scrolling forward in a documentdisplayed on a monitor through five of the scrolling incrementspreviously selected by the user.

Several techniques have been implemented in prior art Z-wheel mice toaddress this performance requirement. One solution is to use amechanical encoder with a built-in detent. In this type of device, amechanical detent is closely coupled with the encoder that produces anelectrical output signal, which satisfies the foregoing performancerequirement. However, mechanical encoders of this type generally costmore than may be desired. Therefore, a less-expensive optical encoderscheme is preferable for accurately detecting rotation of the Z-wheelthrough detent positions.

Optical encoders are commonly used to detect motion and/or position of amember. Two classes of optical encoders are incremental encoders, andabsolute encoders. There are also two types of optical encoders,including rotary encoders and linear encoders. Incremental rotaryencoders are suitable for use in a mouse. Ideally, an incrementalencoder produces a pair (two channels) of square wave signals that areapproximately 90 degrees out of phase; this type of output signal iscommonly referred to as a quadrature output. The quadrature output isprocessed to determine the amount of rotation of an element (such as awheel) monitored by the encoder, and the direction of the element'srotation.

The primary components of a typical optical encoder (prior art) areshown in FIGS. 1 and 2, and include a codewheel or code disk 10, a lightemitter 12, and an integrated detection circuit 14. The codewheelgenerally comprises a plurality of equally-spaced teeth 16, formingslots 18, which may be fully enclosed, or is made from a clear plasticor glass disk imprinted with a radially-spaced pattern of lines,commonly called a “mask.” Light emitter 12 typically comprises an LED20, which emits light rays 21 that are collimated into a parallel beamby a lens 22. Integrated detector circuit 14 is disposed opposite thelight emitter and typically comprises at least two photodetectors 24 (asshown in FIG. 2), or two sets of photodetectors (as shown in FIG. 1),noise reduction circuitry 26, and comparators 28. Suitablephotodetectors include photodiodes and phototransistors.

The codewheel is disposed relative to the light emitter and integrateddetector circuit so that when it is rotated, its slotted or linedportion is between the light emitter and integrated detector circuit.The light beam passing from the light emitter to the integrated detectorcircuit is thus interrupted by the part of the codewheel between thepattern of slots or by the radial lines on the codewheel. Any portion ofthe light beam that is not blocked by the codewheel (or the lines thatare imprinted) is detected by the photodetectors. The photodetectorstypically produce an analog output signal that is proportional to theintensity of light they detect. In general, the output signal producedby each photodetector as the codewheel is turned at a constant rate issinusoidal. The photodetectors are arranged in a pattern that is afunction of the radius and count density of the codewheel, so as toproduce a quadrature output.

In the embodiment shown in FIG. 1, the photodetectors are spaced suchthat a light period on one pair of photodetectors corresponds to a darkperiod on an adjacent pair of photodetectors, thereby producing twocomplimentary outputs for each channel. The photodetector outputs areprocessed by the noise reduction circuitry, which removes extraneousnoise. The resulting four signals are then evaluated by the comparators(one comparator for each complimentary pair of signals), which produce adigital waveform corresponding respectively to channels A and B. Thedigital waveform has voltage levels corresponding to a logic level zeroand a logic level one. If the encoder wheel is turned at a constantangular rate, the output signals on channels A and B will be similar tothe waveforms shown in FIG. 3C, wherein the digital waveform of channelA is approximately 90 degrees out of phase (in quadrature) with channelB. In actual practice, the waveforms are not perfectly square due tosignal propagation delays, switching latencies, etc.—however, thewaveforms approximate square waves.

The quadrature output of an encoder can be evaluated to determine thepresent state of the encoder and the direction that it is being turnedor is moving. FIG. 3B shows a typical state table corresponding to afull quadrature encoding scheme, and the corresponding state transitionsare shown in FIG. 3A. The state of the encoder is dependent on the logicvalue of each channel. For example, if the logic values of channels Aand B are respectively 1 and 0 (represented simply as “(10)”), the stateis 1. By examining changes in the state of the encoder, it is possibleto determine the present position of the encoder by integrating itsincremental motion. A common scheme used to perform this task is shownin FIG. 3C, wherein the state is evaluated at each falling edge of aclock input signal. The direction of rotation of the encoder wheel canalso be determined by determining which channel leads the other, e.g., Aleading B indicates clockwise rotation of the wheel; B leading Aindicates counterclockwise rotation of the wheel.

FIG. 3D shows a state transition table corresponding to the fullquadrature transition states discussed above. The state transition tableindicates when a transition is reported based on a sensed change in theposition of the encoder wheel. In the case of full quadrature encoding,every change in state on either channel produces either a “+” or “−”change in the output produced by processing the channels. Put anotherway, there are two state changes for each change in the output signal ona given channel. As a result, this scheme multiplies the resolution ofthe encoder wheel by four. For an encoder wheel with X teeth, theresolution with which rotation of the wheel can be monitored is 4X.Thus, this type of quadrature encoding is referred to as 4X encoding.

The foregoing optical encoder has several drawbacks when used in a mouseor trackball. A primary problem is that it is too expensive. Eachphotodiode has a finite cost, and the noise reduction circuitry andcomparators also add to the expense of the encoder. Another problem isthat the integrated detector circuit portion of the encoder generallytakes up too much space. Additionally, the level of precision requiredfor an input axis on a mouse is much lower than the level of precisionrequired in other applications that typically often employ opticalencoders of the foregoing design, such as motion controllers, robotics,etc.

In order to address the size and cost limitations of encoders suitablefor use in a mouse, an optical encoder scheme has been developed thatrequires fewer components and is much less costly to manufacture. Anexample of such a scheme is shown in FIG. 4. As shown therein, thedetection circuit has been reduced to a pair of phototransistors 30,each of which produces an analog output signal applied respectively to anon-inverting Schmidt trigger 32. The Schmidt triggers are used tominimize the effects of extraneous noise in the raw signals provided bythe phototransistors. Optionally, other types of comparator circuits canbe used in place of the Schmidt triggers. The output of the Schmidttriggers is input to a microcontroller, which processes the signals onchannels A and B using a special duty-cycle control algorithm to producea digital waveform in quadrature, which is further processed by amicrocontroller to determine the incremental motion imparted to theencoder wheel of the device. Details of the duty-cycle controlalgorithm, which is discussed briefly below, are disclosed in U.S. Pat.No. 5,256,913, the disclosure and drawings of which are herebyspecifically incorporated herein by reference. The output from themicrocontroller is passed through a serial communication link to acomputer (e.g., through an RS-232 serial port, a universal serial busport, or a PS/2 port). A driver in the operating system (or in anapplication program) processes the output from the microcontroller tocontrol the display on the computer screen in response to the movementof the encoder wheel.

As might be expected, the waveforms produced by thephototransistor/Schmidt trigger/duty-cycle control algorithm scheme arenot as accurate and clean as the waveforms produced by the detectioncircuit of FIG. 1. Due to the lower accuracy of the waveforms, there isa higher probability that a logic level change (a transition between ahigh and low voltage level) on a channel might be missed, or that afalse logic level change might be indicated—either of which would causethe movement of the encoder wheel to be inaccurately reflected in thecontrol action implemented by the computer. To overcome this problem, anew state transition scheme was developed as shown in FIGS. 5A and 5B.In this state transition scheme, there are two electrical state changesrequired for each detent position of the encoder wheel, which reducesthe impact of missed state transitions and false signals, but is stillsusceptible to several troublesome problems when used with a detentedcontrol wheel.

A more detailed view of the prior art detented wheel/optical encoderassembly shown in FIG. 2 is illustrated in FIG. 6. The assembly includesa wheel 50 mounted on a shaft 52, which is supported at one end by abearing 54 in a support bracket 56, and at an opposite (free) end by ametal coil spring 58, which is displaced over a post (not shown).Lateral movement of the shaft is restricted by a slot 60 defined in aslotted bracket 62, through which the shaft extends. Support bracket 56,the spring post, and slotted bracket 62 all extend upwardly from theinterior surface of a lower case 64. Coil spring 58 and slot 60 allowthe free end of the shaft to pivot in bearing 54 (which is slightlyelongated in the vertical direction to allow for such pivoting),permitting the wheel to be vertically displaced when a downward force isapplied to it. This vertical displacements enables a collar 66 formed inthe shaft to actuate a microswitch (not shown) mounted beneath thecollar. The actuation of the microswitch by a user changes a scrollingmode of the display. An upward force provided by coil spring 58 biasesthe free end of the shaft upwardly away from the microswitch when thedownward force on the wheel is removed. Formed as an integral part ofthe shaft is a codewheel 10, with a plurality of teeth 16 defining slots18 (shown in FIG. 1), as discussed above. The teeth and slots passbetween light emitter 12 and phototransistors 24 (see FIGS. 1 and 2),which are mounted in a detector housing 68. The detector housing and thelight emitter are mounted to a common base 70, which clips into aprinted circuit board (PCB) 72 and defines a location hole 74 that isused to locate the base relative to an alignment pin 76 extending fromthe interior surface of the lower case.

The assembly produces a detent action through the use of a metal leafspring 78, which has a protrusion 80 formed on its upper free end. Thisprotrusion rides against a splined portion 82 of the shaft comprising aplurality of spline teeth separated by spline wells. The lower fixed endof the metal leaf spring is mounted to support bracket 56 (at a pointdisposed under the PCB). As the shaft is rotated, the protrusion ridingon the splined portion of the shaft causes the spring to flex, therebycreating a detent action.

The force required to move the wheel from one detent position to thenext varies with the angular position of the wheel as it is rotatedbetween the detent positions. FIG. 7 illustrates the relativedisplacement of the protrusion 80 with respect to the spline teeth asthe shaft 52 is rotated. The force the leaf spring exerts on the hubvaries linearly with this displacement. As the wheel is rotated,protrusion 80 moves in and out of the spline wells and over the splineteeth, thereby changing the pressure angle (i.e., the angle of thenormal surface at the contact point) between the protrusion and a splinetooth. Assume the leaf spring is configured to be displaced in avertical direction. In general (without considering friction), for agiven amount of wheel torque, the vertical component of the force actingon the leaf spring (i.e., causing the leaf spring to flex) isproportional to the vertical component of the pressure angle. As aresult, the maximum amount of torque encountered when rotating the wheelbetween detent positions occurs immediately after leaving a detentposition, as shown in FIG. 15. Additionally, as the wheel is furtherrotated, the torque needed to rotate the wheel will become negative asthe protrusion slides over the top of a spline tooth, thereby causingthe wheel to move forward into the next detent position as the springbias force causes the protrusion to slide into the next spline well.

Under optimal circumstances, there should be a tendency for the wheel toalways return to a detent position if a user releases the wheel (stopsapplying a rotational force to the wheel), regardless of the angularposition of the wheel when released. However, as shown in each regionenclosed by an ellipse in FIG. 7 and in FIG. 8, there are areas betweendetent positions, known as balance areas, where the wheel will hang andnot return to a detent position if it is released, i.e., if the userstops applying a rotational force to the wheel. (If the wheel isreleased outside of one these balance areas, the wheel will always moveto the nearest detent position, as is desired.) Due to variations infriction caused by non-symmetrical spring geometry, the balance pointfor rotation of the wheel in a forward direction is not necessarilycoincident with the balance point for rotation of the wheel in a reversedirection.

FIG. 7 also illustrates another problem that can be encountered with adetented optical encoder, known as bounce back. Bounce back occurs whena user turns or rolls the wheel forward quickly and then releases thewheel just prior to passing through a balance point to the next detentposition. If the wheel has been rolled forward rapidly, it is possiblefor the wheel to continue rolling for a short duration in its presentdirection after the user has stopped turning the wheel, due to theangular momentum of the encoder wheel. The wheel will slow down, stop,then return to the previous detent position. If the electrical systemsenses a transition point prior to the direction of wheel rotationreversing, the result will be that the last electrical count is reportedin a direction opposite that in which the user was rolling the encoderwheel. This problem will be more clearly understood from the followingexplanation.

At position A, the encoder wheel is moving forward and a forwardtransition is reported, as indicated by a “+.” At position B, theencoder wheel is moving forward and a second forward transition isreported. Between positions B and C, the user stops turning the encoderwheel, but the angular momentum causes the encoder wheel to continuerolling forward. At position C, the encoder wheel is rotating forwardvery slowly, but a forward transition is reported. Just after positionC, the encoder wheel stops; it then changes direction, and returns tothe previous detent position. However, at position D, the encoder wheelis rotating in the reverse direction, and a transition in the reversedirection is reported. At position E, the encoder wheel comes to rest.As a result of the preceding scenario, an extra forward transition andan extra reverse transition are registered by the encoder, even thoughthe user did not intend the transitions C+ and D− to be registered.These erroneous transition registrations can be quite bothersome,especially if a user is working on a relatively slow computer on which alag time between the instant when a scrolling request is received andthe instant that the display or data actually scrolls is very evident.In such a case, the user is forced to wait for the false forward andreverse transitions to be implemented on the display before continuingto work on the document or data.

Ideally, the reporting of a transition state change indicating a usermovement of the wheel to a new detent position (called the transitionpoint) should occur just after passing the balance region. At thispoint, it is certain that the encoder wheel will move to the next detentposition if the user releases (stops turning) the wheel, and bounce backcannot occur. In addition, it is preferable that the reported transitionpoint (i.e., the angle at which the encoder wheel is when a transitionis reported) for both a forward and reverse encoder wheel rotationoccurs at repeatable positions.

It is not practical to achieve the ideal operation in the prior artencoder wheel design discussed above, due to part and assembly variancescommonly associated with the manufacture of large lots of this type ofproduct. For example, a variation of a mere 0.001″ in the location ofthe protrusion on the leaf spring results in a 0.5 (ATAN [0.001/0.117])degree shift in the transition angle. Other examples of the adverseeffect of manufacturing variances include the variation in the distancebetween the point on the support bracket to which the leaf spring ismounted and the center of bearing 60 in the support bracket, and thevariation in the location of the alignment pin relative to the bearing.The variation in the dimensions within reasonably achievablemanufacturing tolerances of the various parts comprising the encoderassembly and/or the variation in the assembled position of these partscan add together to cause the angular position of the teeth/slots to beoutside the specified tolerance. Thus, the reported transition pointswill be out of tolerance relative to the detent positions. In order tomeet the desired performance requirement, the tolerances on the partsthat comprise the prior art assembly would have to be so tight that thecost of fabricating this assembly would be prohibitive.

Furthermore, in the prior art design, the location of some of thecomponents may change over time, due to creep and/or wear. For example,the leaf spring constantly applies a lateral force to the supportbracket, which eventually may cause the location of the bearing tocreep, i.e., shift relative to the rest of the case. As a result, thelocation of the codewheel relative to the light emitter andphotodetector may shift, causing the transition point to shift as well.Another problem occurs as a result of wear on the contacting surfacesand/or fatigue in the leaf spring. As a result, the mechanical accuracyof the detent positions relative to the encoder signal output in a givenassembly may change over time. In consideration of these and otherproblems related to accurately detecting transitions as the encoderwheel is rotated, acceptable angular ranges 90 and 92 shown in FIG. 9have been specified for the occurrence of a transition point relative tothe adjacent detent positions.

Another problem with the prior art design is that the metal in the leafspring and coil spring can provide a conduit for an electrostaticdischarge (ESD) to susceptible internal components, which may adverselyaffect the electrical components of the pointing device or of thecomputer to which the device is coupled.

It would therefore be desirable to provide a detented optical encodercontrol device that avoids the problems of the prior art devicesdiscussed above. Such a device should eliminate or minimize the effectsof bounce back, should avoid using component that can cause ESD, andshould enable components to be used for the device that are ofacceptably low cost and do not require unreasonably tight tolerances orrequire costly assembly procedures.

SUMMARY OF THE INVENTION

The invention provides a solution to the foregoing problems by replacingmuch of the prior art assembly with a single spring biased member, whichis referred to herein as an “opto spacer.” The opto spacer includesmeans for locating the light emitter and photodetector (i.e.,phototransistors) relative to detent positions of the codewheel suchthat the output signal from the photodetector that is indicative of thedetent positions is much more consistent. Furthermore, the opto spacer,which is preferably made from a plastic, carries out the functions ofboth the metal leaf spring and metal coil spring used in the prior artdesign, thereby removing two potential sources of ESD.

According to a first aspect of the invention, a detented encodersuitable for use in a computer input device such as a mouse is providedcomprising conventional optical encoder components including a lightsource (preferably an LED with appropriate lens), a light sensor (i.e.,photodetector), and a codewheel. The light source directs light at thelight sensor, which preferably comprises a pair of phototransistors orphotodiodes. The codewheel includes a plurality of radially-extending,evenly spaced-apart teeth that define slots, and the codewheel ispositioned such the teeth and slots are disposed between the lightsource and light sensor. Upon rotation of the codewheel, the teethinterrupt the light from the light source reaching the light sensor. Thecodewheel is mounted on a shaft (or preferably the shaft and codewheelare formed as an integral part) that includes a portion having aplurality of longitudinally extending slots defined in a surfacethereof. Mounted to the shaft is the wheel that is turned by a user. Theshaft is supported at one end by a bearing surface defined in a supportbracket that is coupled to a support member.

A key component of the invention is the opto spacer, which is preferablymade of plastic and operatively coupled to the support member,preferably by being mounted to a printed circuit board (PCB), which inturn is mounted to the support member. The opto spacer is preferablymounted to the PCB by legs that engage holes defined in the PCB andincludes a base portion that provides an alignment hole mated with analignment pin extending from the support member through the PCB so as tolocate the opto spacer relative to the support member. The base portionof the opto spacer also preferably includes alignment holes for locatingthe light source and light sensor.

The opto spacer further comprises a cantilever portion connected to thebase portion by a pair of elastomeric arms, thereby enabling thecantilever portion to apply a biasing force against the shaft when thearms are flexed. The cantilever portion comprises a U-shaped openingthat is sized to receive the splined portion of the shaft and includes aprotrusion disposed generally in its center. The protrusion engages aspline in the splined portion of the shaft. The biasing force exerted bythe cantilever portion through the protrusion provides a pre-loadagainst the splined portion of the shaft such that when the shaft isrotated by the wheel, the cantilever portion flexes as the protrusionmoves in and out of spline wells defined between adjacent spline teeth,thereby producing a detent action that defines a plurality of detentpositions at equally-spaced angles of rotation corresponding to theplurality of spline teeth in the splined portion of the shaft. Thecantilever portion of the opto spacer may further comprise a pair ofbearing surfaces located on the far side of the opening that bearagainst an adjacent surface on the front side of the support bracketsuch that when the cantilever portion is caused to flex by the detentaction, the movement of the cantilever portion is in a directionsubstantially transverse to the longitudinal axis of the shaft.

The detented encoder further preferably comprises a slotted bracketconnected to the support member that includes a slot sized to receivethe free end of the shaft and to control a lateral displacement of thefree end of the shaft. The slot in the slotted bracket preferablypermits movement of the shaft so as to enable a user to activate aswitch located adjacent to the shaft when the user applies a force onthe wheel directed toward the switch.

The detented encoder also preferably includes a logic circuit that isused to process a quadrature signal produced by the photodetector. Thequadrature signal is processed by the logic device to produce an outputsignal indicative of the direction and number of detent positions thewheel is turned by the user. A transition between adjacent detents isreported at a point where rotation of the codewheel to the next detentposition is certain to occur if the user releases the wheel, therebysubstantially avoiding the problems associated with bounce back.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a conventional prior art opticalencoder that incorporates four photodetectors;

FIG. 2 is an isometric view of an assembly comprising the primarycomponents of a prior art detented optical encoder;

FIGS. 3A and 3B respectively show a state transition diagram and itsassociated state table corresponding to a conventional full-quadratureencoding scheme;

FIG. 3C shows a scheme for evaluating the states of a conventionalquadrature signal;

FIG. 3D shows a transition state table corresponding to a conventional4X quadrature encoding scheme;

FIG. 4 is a schematic diagram of a low-cost optical encoder suitable foruse in the present invention;

FIG. 5A is a state diagram corresponding to a 2X quadrature encodingscheme used with the optical encoder of FIG. 4;

FIG. 5B is a transition state table corresponding to the state diagramof FIG. 5A;

FIG. 6 shows an isometric view of a Z-wheel mouse comprising a prior artdetented optical encoder assembly;

FIG. 7 is a force curve corresponding to a relative level of force vs.angle encountered when turning a detented wheel through a plurality ofadjacent detents;

FIG. 8 is a diagram illustrating a balance area that may exist betweentwo adjacent detents;

FIG. 9 is a diagram specifying an allowable angular range for thereporting of a transition point between detents;

FIG. 10 is a rear isometric view of the detented optical encoderassembly of the present invention;

FIG. 11 is a front view of the assembly of FIG. 10;

FIG. 12 is a rear isometric view of the assembly of FIG. 10, with thewheel, codewheel, and shaft removed;

FIG. 13 is a detailed underside isometric view of the opto spacer usedin the assembly of FIG. 10; and

FIG. 14 is a process diagram illustrating how the effect of bounce backis substantially eliminated by the present invention.

FIG. 15 is a composite torque vs. angle and friction force vs. anglegraph corresponding to the torque and friction encountered when rotatingthe wheel between adjacent detent positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 10 and 11, it will be apparent that the detentedencoder of the present invention includes many of the same componentsdiscussed above in connection with the prior art detented wheel/opticalencoder assembly of FIG. 6, including slotted bracket 62, light emitter12 and photodetectors 24. There are also many components common to bothassemblies that are substantially similar in purpose, but differ inconfiguration or in the manner in which they function. These componentsare identified in the Figures by appending an “A” to each component'sreference number, and include a wheel 50A, a shaft 52A, a supportbracket 56A, a case 64A, and spline teeth 82A, which extendlongitudinally along shaft 52A. A new codewheel 110 has been substitutedfor codewheel 10 shown in FIGS. 2 and 6.

There are several important differences between the assembly of thepresent invention shown in FIGS. 10 and 11 and the prior art assemblyshown in FIGS. 2 and 6. Notably, the new design of the present inventiondoes not include a metal leaf spring or a coil spring. Both of thefunctions previously performed by the leaf and coil springs of the priorart design are now provided by a biasing member 112, which is alsoreferred to herein as an opto spacer; further details of the opto spacerare shown in FIGS. 12 and 13. The opto spacer is preferably injectionmolded with a polycarbonate plastic, and more preferably made of BAYERAPEC DP99 351R1510 or an equivalent plastic material. The opto spacercomprises a base portion 114 and a cantilever portion 116. A U-shapedopening 118 defined by upright members 119 is provided in an upperportion of the cantilever portion, and a protrusion 120 is disposedgenerally in the center of U-shaped opening 118. The cantilever portionadditionally comprises a pair of elastomeric arms 122 that extend frombase portion 114. Elastomeric arms 122 allow cantilever portion 116 todeflect relative to the base portion in response to the application of aforce acting on the cantilever portion.

As shown in FIGS. 10 and 11, the width of U-shaped opening 118 in theopto spacer is sufficient to receive the splined portion of the shaft.Furthermore, the protrusion is designed to engage the spline teeth suchthat the elastomeric arms are caused to be flexed by a movement of theprotrusion (and the entire cantilever portion) as the protrusion movesin and out of successive spline wells defined between adjacent splineteeth when the wheel is turned, thereby creating a detent action. Due tothe even spacing of the slots around the circumference of the slottedportion of shaft 52A, the interaction between the protrusion and thespline teeth (and spline wells) creates a plurality of equally-spaceddetents as the wheel is turned. These detents are preferably spaced atabout 20 degrees apart. Upright members 119 limit lateral movement ofthe cantilever portion due to the side load imparted through theprotrusion as the wheel turns.

It is preferable that an appropriate lubricant (such as a syntheticgrease) be applied to the splined portion of the shaft in the vicinityof the protrusion so as to minimize wear as the protrusion slides overthe ridges of successive spline teeth 82A. Preferably, the cantileverportion further includes a pair of rubbing blocks 124 disposed on itsbackside, just adjacent to upright members 119; the spacing between theopto spacer and support bracket 56A is such that the rubbing blocks arein light contact with an adjacent front surface 125 of the supportbracket as the cantilever portion moves up and down. The sliding contactbetween rubbing blocks 124 and front surface 125 constrains the movementof the cantilever portion to be substantially vertical, enabling theprotrusion to remain parallel with the spline teeth in the shaft. (Itshould be noted that as used in this disclosure and in the claims thatfollow, the directions “vertical,” “horizontal,” “up,” and “down” areall relative to the disposition of the elements shown in the Figures,and these directions are readily changed simply by mounting thecomponents so that they are oriented differently than shown in thedrawing Figures. Accordingly, the directions used herein are notintended to be limiting on the scope of this invention.) Preferably, anappropriate lubricant (such as a synthetic grease) is also appliedbetween the rubbing blocks and the adjacent support bracket frontsurface to reduce wear of these components.

In addition to the foregoing, the opto spacer also serves the purposepreviously provided by the coil spring that was used in the prior artdesign discussed above. The opto spacer applies an upwardly directedforce through the protrusion to the shaft that biases the free end ofthe shaft away from a microswitch 126. Since the elastomeric arms of thecantilever portion can easily flex, a user applying a light downwardpressure on the wheel causes shaft 52A to activate microswitch 126. Whenthe downward pressure is released, the elastomeric arms return the freeend of the shaft back to its normal position above the microswitch.

With reference to FIG. 13, a plurality of holes defined in the optospacer for alignment purposes are illustrated, including a casealignment hole 129, detector alignment holes 128, and light emitteralignment holes 130. The opto spacer further includes alignment pins132, a detector clip 134, a light emitter clip 136, and PCB clips 138.Case alignment hole 129 is disposed to align the opto spacer with analignment pin 76A (shown in FIG. 11) extending from an inner surface ofthe lower case. Detector alignment holes 128 receive leads 140 (shown inFIG. 12), which extend from the bottom of the detector housing.Similarly, light emitter alignment holes 130 receive a pair of leads(not shown) extending from the bottom of the light emitter. The detectorand light emitter clips engage the detector housing and the lightemitter respectively, securing them in place. The alignment pins alignthe opto spacer with alignment holes provided in the PCB, and the clipsmount on the PCB.

The opto spacer design solves many of the problems in the prior artdevice of FIGS. 2 and 6 discussed above. First, because the opto spaceris a single integral piece, the tolerance stack-up problems associatedwith the prior art assembly are substantially eliminated. For example,the lateral disposition of the protrusion relative to the location ofthe alignment holes for the light emitter and photodetectors is veryconstant in the present invention, with only a very slight (acceptable)variation between lots of parts. Since the inside of U-shaped opening118 in the cantilever portion, i.e., arms 119, is in rotating contactwith the outer surfaces of the ridges between spline teeth 82A on theshaft, the lateral position of the protrusion relative to the shaftremains very constant, and therefore, the lateral position of theprotrusion relative to the light emitter and photodetector while in adetent position will be much more consistent from assembly to assembly.The relative position, lateral and angular, between the encoder teethand the opto pair predominantly depends only on the tolerances within asingle part (opto spacer) and very little on the placement of the optospacer within an assembly. This consistency enables the specified rangefor the transition angle to be smaller, thereby minimizing theoccurrence of bounce back, as discussed below. In addition, theelimination of the metal leaf and coil springs in the present inventioneliminates any ESD that was associated with these metal components inthe prior art designs.

The opto spacer design provides another advantage by minimizing problemsdue to creep. Recall that in the prior art design, the metal leaf springapplies a constant side load to the support bracket (through the shaft),which may cause the location of the bearing to creep (be slightlydisplaced) in a lateral direction over time, thereby causing theposition of the shaft (and thus the codewheel) to shift correspondingly.While the cantilever portion of the opto spacer likewise applies aconstant load to the support bracket (through the shaft), this load isapplied vertically. Furthermore, the load on the bearing in the optospacer design of the present invention is about half that of the priorart design. Finally, any creep caused by this load will have less effecton the accuracy of the reporting of transition points relative to detentpositions because the shaft and codewheel are displaced vertically,rather than laterally.

A further advantage provided by the opto spacer design of the presentinvention is that the “feel” of the wheel (i.e., the amount of torquerequired to move the wheel between detent positions) may be easilyadjusted. Such an adjustment is made by simply changing the geometry ofthe protrusion and/or the geometry of the profile of the spline teeth.

With reference to FIG. 14, it will be evident that the detented encoderassembly of the present invention can be combined with specializedsignal processing to ensure that the reported transition points betweenadjacent detents occurs substantially only after the passing ofbalancing points. The processing starts with the output produced by anoptical encoder circuit 200, which is shown in FIGS. 10 and 11 andincludes the components discussed above, with reference to FIG. 4. Theoptical encoder circuit produces a pair of sinusoidal output signals 202and 204 on respective channels A and B when the wheel (and thus thecodewheel) is rotated at a constant rate; the phase angle betweenchannels A and B is approximately 90 degrees. The number of spline teeth82A in shaft 52A are preferably equal to the number of teeth defined inthe codewheel (or an integer multiple thereof) so that the phase anglebetween the sinusoidal output signals produced on channels A and Bremain constant relative to the location of physical detents 205 as thewheel is turned.

A logic device 206 is preprogrammed with logic to process sinusoidaloutput signals 202 and 204 on channels A and B, producing correspondingsquare waves 208 and 210, respectively, which comprise a quadraturesignal. The logic device further includes a state transition table 212that includes a plurality of entries defining when transitions in theposition of the wheel should be reported based on changes in the logiclevels of channels A and B. The logic device uses the transition statetable to generate data 214 concerning the present incremental positionof the encoder, which are reported within a specified angular rangebetween detents as the wheel is turned by a user. Details of theprocessing performed by the logic device and the state transition tableare disclosed in a commonly assigned copending application entitled, “AMETHOD FOR DETERMINING THE POSITION OF A DETENTED OPTICAL ENCODER,” Ser.No. , 09/442,592, filed on Nov. 17, 1999, the disclosure of thespecification and drawings of which is hereby specifically incorporationherein incorporated by reference.

As discussed above, the opto spacer design results in much higherconsistency in the location of the various assembled components on anassembly-by-assembly basis. Furthermore, since the effect of creep isminimized, the angle at which transition points are reported relative tophysical detent positions for a given assembly changes very little overtime. As a result, it is possible to narrow the specified reportedtransition point range discussed above in reference to FIG. 9 such thatreported transition points substantially only occur after a balancepoint has been passed as the wheel is turned between adjacent detentpositions.

As shown in a force curve 216 of FIG. 14 (similar to the force curvediagram shown in FIG. 7), reported transition points 218 now occur afterbalance regions 220 have been passed. For example, when moving the wheelforward from a detent 222 to an adjacent detent 224 in the presentinvention, a “+” count is reported at a position A′, in contrast toreporting the “+” count at a position A, as was the case with the priorart design discussed above with reference to FIG. 7. Likewise, a “+”count is reported at position B′ when the wheel is turned forward to thenext detent. As with the previous description of bounce back, when thewheel is turned from position B to position C the user releases thewheel, but the wheel continues to roll forward due to its angularmomentum. At position C, the wheel is moving forward very slowly, but inthis case, the logic device does not report a forward count because abalance point 226 has not yet been passed. Just after position C, thewheel stops rotating in the forward direction, changes direction, andreturns to the last detent at position E. At position D, the wheel isrolling in the reverse direction, but the logic device again does notreport a reverse count, since the encoder wheel did not pass throughbalance point 226 in the reverse direction. At position E the wheelcomes to rest at a detent. Thus, since neither a forward nor a reversetransition (i.e., count) is reported at either of positions C or D, theprevious problem with bounce back has been substantially eliminated (orat least minimized—the actual transition point will vary depending onthe sensitivity of the optical encoder circuit, so there may beinstances where an overlap occurs between allowed transition points andbalance points).

Although the present invention has been described in connection with thepreferred form of practicing it, those of ordinary skill in the art willunderstand that many modifications can be made thereto within the scopeof the claims that follow. Accordingly, it is not intended that thescope of the invention in any way be limited by the above description,but instead be determined entirely by reference to the claims thatfollow.

The invention in which an exclusive right is claimed is defined by thefollowing:
 1. A detented encoder employed for sensing a rotation of awheel by a user, comprising: (a) a rotatable shaft on which the wheel ismounted, said shaft having a splined portion that includes a pluralityof evenly-spaced, longitudinally extending spline teeth defined about asurface thereof; (b) a light source; (c) a light sensor that produces asignal indicative of an intensity of light received from the lightsource; (d) a support having a bearing surface in which the shaft isrotatably mounted; (e) a biasing member, operatively coupled to thesupport and including: (i) a base portion on which the light source andthe light sensor are mounted; and (ii) a cantilever portion connected tothe base portion and applying a pre-load force against the splinedportion of the shaft, said cantilever portion including a protrusiondisposed adjacent to the splined portion of the shaft and engaging aspline tooth from among the plurality of spline teeth in the splinedportion, the pre-load force provided by the cantilever portion beingapplied through the protrusion against the splined portion of the shaftsuch that when the shaft is rotated by the wheel, the cantilever portionflexes as the protrusion moves in and out of spline wells definedbetween adjacent spline teeth, thereby producing a detent action thatdefines a plurality of detent positions at equally-spaced angles ofrotation corresponding to the plurality of equally-spaced spline teeth;and (f) a codewheel mounted on the shaft and having a plurality ofradially-extending, circumferentially spaced-apart teeth between whichare defined slots, said teeth passing between the light source and thelight sensor when the wheel is turned and rotates the shaft, whichrotates the codewheel, said teeth interrupting the light received by thelight sensor from the light source so that the signal produced by thelight sensor is indicative of the rotation of the wheel.
 2. The detentedencoder of claim 1, wherein the cantilever portion comprises a pair ofelastomeric arms extending from the base portion.
 3. The detentedencoder of claim 1, wherein the biasing member comprises a plastic.
 4. Adetented encoder employed for sensing a rotation of a wheel by a user,comprising: (a) a rotatable shaft having a supported end and a free end,and a splined portion that includes a plurality of evenly-spaced,longitudinally extending spline teeth defined about a surface thereof,said wheel being mounted on the shaft; (b) a supporting member; (c) alight source; (d) a light sensor that produces a signal indicative of anintensity of light received from the light source; (e) a bracketconnected to the supporting member and having a bearing surface definedtherein in which the supported end of the shaft is rotatably mounted;(f) a biasing member, operatively coupled to the supporting member andincluding: (i) a base portion on which the light source and the lightsensor are mounted; and (ii) a cantilever portion connected to the baseportion and applying a biasing force against the splined portion of theshaft, said cantilever portion comprising: (1) a U-shaped openingadapted to receive the splined portion of the shaft; and (2) aprotrusion disposed generally in a center of the opening, to engage aspline tooth of the plurality of spline teeth in the splined portion ofthe shaft, the cantilever portion providing the biasing force throughthe protrusion as a pre-load against the splined portion of the shaftsuch that when the shaft is rotated by the wheel, the cantilever portionflexes as the protrusion moves in and out of spline wells definedbetween adjacent spline teeth, thereby producing a detent action thatdefines a plurality of detent positions at equally-spaced angles ofrotation corresponding to the equally spaced-apart spline teeth; and (g)a codewheel mounted on the shaft and having a plurality ofradially-extending, circumferentially spaced-apart teeth between whichare defined slots, said teeth passing between the light source and thelight sensor when the wheel is turned, rotating the shaft, which rotatesthe codewheel, said teeth interrupting the light received by the lightsensor from the light source so that the signal produced by the lightsensor is indicative of the rotation of the wheel.
 5. The detentedencoder of claim 4, wherein the cantilever portion comprises a pair ofelastomeric arms extending from the base portion.
 6. The detentedencoder of claim 4, wherein the biasing member comprises a plastic. 7.The detented encoder of claim 4, further comprising a slotted bracketconnected to the supporting member and having defined therein a slotthat receives the free end of the shaft, said slot controlling a lateraldisplacement of the free end of the shaft.
 8. The detented encoder ofclaim 7, further comprising a switch disposed adjacent to the shaft,wherein the slot in the slotted bracket allows the shaft to be displacedso as to activate the switch upon application of a force on the wheel ina direction aligned with the slot in the slotted bracket.
 9. Thedetented encoder of claim 4, wherein the supporting member includes alocating pin, and the base portion of the biasing member includes alocation hole that receives the locating pin to control a disposition ofthe biasing member relative to the supporting member.
 10. The detentedencoder of claim 4, wherein the base portion of the biasing memberdefines a plurality of locating holes for mounting the light source andthe light sensor, such that a disposition of the light source relativeto the light sensor, and a disposition of the light source and the lightsensor relative to the biasing member is controlled.
 11. The detentedencoder of claim 4, wherein the base portion of the biasing memberincludes a clip for retaining the light source.
 12. The detented encoderof claim 4, wherein the base portion of the biasing member includes aclip for retaining the light sensor.
 13. The detented encoder of claim4, further comprising a printed circuit board mounted to the supportingmember, wherein the biasing member includes at least one leg received ina respective hole in the printed circuit board to mount the biasingmember onto the circuit board.
 14. The detented encoder of claim 4,wherein the cantilever portion of the biasing member comprises a bearingsurface disposed adjacent to the bracket, the bearing surface actingagainst the bracket when the cantilever portion is caused to flex by thedetent action, to limit a movement of the cantilever portion in adirection substantially transverse to a longitudinal axis of the shaft.15. The detented encoder of claim 4, wherein the light sensor comprisesa pair of photodetectors that are spaced apart at a distance based on awidth of the slots in the codewheel such that the light sensor producesa quadrature output when the wheel is turned.
 16. The detented encoderof claim 15, wherein the light source comprises a light emitting diodeand the photodetectors each comprise a phototransistor.
 17. The detentedencoder of claim 15, further comprising a logic device that processesthe quadrature output to produce data indicative of a detent positionwhen the wheel is turned.
 18. A detented encoder employed in a pointingdevice, for sensing a detent position of a wheel when the wheel isturned by a user, comprising: (a) a horizontally-disposed rotatableshaft having a supported end, a free end, and a splined portion thatincludes a plurality of evenly-spaced, longitudinally extending splineteeth defined about a surface thereof, said wheel being mounted on theshaft; (b) a support member; (c) a light source; (d) a photodetectioncircuit comprising a pair of light sensors, each light sensor of saidpair producing a signal indicative of an intensity of light receivedfrom the light source by that light sensor; (e) a logic device coupledto the photodetection circuit; (f) a bracket connected to the supportmember and having a bearing surface defined therein to rotatably mountthe supported end of the shaft; (g) a slotted bracket connecting to thesupport member and having defined therein a slot that receives the freeend of the shaft, said slot controlling a lateral displacement of thefree end of the shaft; (h) a biasing member, operatively coupled to thesupport member and including: (i) a base portion on which the lightsource and the light sensors are mounted; and (ii) a cantilever portionconnected to the base portion and applying a biasing force against thesplined portion of the shaft, said cantilever portion comprising: (1) aU-shaped opening adapted to receive the splined portion of the shaft;and (2) a protrusion disposed generally in a center of said opening, toengage a spline tooth from among the plurality of spline teeth in thesplined portion of the shaft, the cantilever portion being sufficientlyelastomerically displaced to provide a vertical pre-load through theprotrusion against the splined portion of the shaft such that when theshaft is rotated by the wheel, the cantilever portion flexes as theprotrusion moves in and out of spline wells defined between adjacentspline teeth, thereby producing a detent action that defines a pluralityof detent positions at equally-spaced angles of rotation; and (i) acodewheel mounted on the shaft and having a plurality ofradially-extending teeth between which are defined slots, said teethpassing between the light source and the light sensors as the rotationof the wheel rotates the shaft, which rotates the codewheel, said teethinterrupting the light received by the light sensors from the lightsource so that signals produced by the photodetection circuit andprocessed by the logic device to produce a quadrature signal areindicative of the detent position of the wheel when the wheel is turnedby the user.
 19. The detented encoder of claim 18, further comprising aswitch disposed under the shaft, wherein the slot in the slotted bracketallows the shaft to be vertically displaced so as to activate the switchupon application of a downward force on the wheel by the user.
 20. Thedetented encoder of claim 18, wherein the pointing device one of a mouseand a trackball.